:root {
    --bg-color: #121212;
    --surface-color: #1e1e1e;
    --primary-yellow: #FFD54F;
    --primary-yellow-hover: #FFC107;
    --primary-green: #81C784;
    --primary-green-hover: #66BB6A;
    --danger-color: #FF5252;
    --danger-hover: #FF1744;
    --text-main: #E0E0E0;
    --border-color: #FFFFFF;
    --border-width: 3px;
    --shadow-size: 6px;
}

* {
    box-sizing: border-box;
    border-radius: 0 !important; /* Tuyệt đối không bo góc */
}

body {
    margin: 0;
    padding: 30px 15px;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.6;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 30px;
}

/* Khối hộp phẳng, đổ bóng cứng */
.block-box {
    background-color: var(--surface-color);
    border: var(--border-width) solid var(--border-color);
    padding: 25px 35px;
    box-shadow: var(--shadow-size) var(--shadow-size) 0px var(--primary-yellow);
}

.login-box {
    max-width: 400px;
    margin: 100px auto 0;
    text-align: center;
}

.top-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background-color: var(--surface-color);
    border-bottom: var(--border-width) solid var(--primary-yellow);
}

h1 { margin: 0 0 10px 0; font-size: 26px; text-transform: uppercase; letter-spacing: 2px; color: var(--primary-yellow); }
h2 {
    background-color: var(--primary-green);
    color: #121212;
    border: var(--border-width) solid var(--border-color);
    padding: 8px 15px;
    margin-top: 0;
    margin-bottom: 20px;
    text-transform: uppercase;
    font-size: 18px;
    display: inline-block;
}

input[type="text"], input[type="password"], select, input[type="file"] {
    width: 100%;
    padding: 10px;
    margin-bottom: 15px;
    background-color: #2c2c2c;
    color: var(--text-main);
    border: 2px solid var(--border-color);
    font-size: 14px;
    outline: none;
}
input:focus, select:focus { border-color: var(--primary-yellow); }

.control-group { display: flex; gap: 10px; margin-bottom: 10px; }
.control-group input, .control-group select { margin-bottom: 0; flex-grow: 1; }

.btn {
    display: inline-block;
    background-color: var(--primary-green);
    color: #121212;
    padding: 10px 20px;
    font-weight: bold;
    text-transform: uppercase;
    border: 2px solid var(--border-color);
    cursor: pointer;
    transition: all 0.1s ease-in-out;
    width: 100%;
}
.btn:hover { background-color: var(--primary-green-hover); transform: translate(-2px, -2px); box-shadow: 4px 4px 0px var(--border-color); }
.btn:active { transform: translate(2px, 2px); box-shadow: 0px 0px 0px var(--border-color); }

.btn-danger { background-color: var(--danger-color); color: #fff; width: auto; }
.btn-danger:hover { background-color: var(--danger-hover); box-shadow: 4px 4px 0px var(--primary-yellow); }

.btn-warning { background-color: var(--primary-yellow); width: auto; }
.btn-warning:hover { background-color: var(--primary-yellow-hover); }

.session-info { display: flex; align-items: center; gap: 15px; font-weight: bold; font-size: 18px; color: var(--primary-yellow); }
.status-msg { margin-top: 10px; font-size: 14px; font-weight: bold; color: var(--primary-yellow); }