phpmailerTest/styles.css

* {
    box-sizing: border-box;
}

:root body {
    font-size: 16px;
    line-height: 22px;
    margin: 0;
    padding: 16px 32px;
}

h1 {
    font-size: 26px;
    font-weight: bold;
}

h2 {
    font-size: 20px;
    font-weight: bold;
}

.bold {
    font-weight: bold;
}

.notice {
    font-weight: bold;
    color: red;
    text-align: center;
    line-height: 22px;
}

/* form styles */
.form {
    align-items: center;
    display: flex;
    flex-direction: column;
    margin: 32px auto;
}

.form > div {
    margin: 4px 0;
    padding: 4px;
    width: 50%;
}

.form p {
    font-weight: bold;
    margin: 0 0 8px;
    text-transform: capitalize;
}

.btn {
    background-color: transparent;
    border: 1px solid black;
    font: inherit;
    margin: 0 4px;
    padding: 8px 32px;
    transition: all 0.25s ease;
    width: 25%;
}

.btn:hover,
.btn:focus {
    background-color: black;
    color: white;
}

.radioLabel,
.textLabel {
    align-items: baseline;
    display: flex;
}

.radioLabel {
    margin-bottom: 8px;
}

.textbox {
    border-bottom: 1px solid #ababab;
    border-left: none;
    border-right: none;
    border-top: none;
    flex: 1;
    font: inherit;
    margin-left: 8px;
    outline: none;
}

.textLabel {
    margin-bottom: 16px;
}

/* form: addresses section */
.addresses {
    display: flex;
    flex-direction: column;
    padding: 16px 8px;
}

/* form: buttons section */
.buttons {
    display: flex;
    justify-content: center;
}

/* form: options section */
.options {
    display: flex;
    justify-content: space-evenly;
}

.encryptionSelect {
    display: flex;
    flex-direction: column;
    justify-content: start;
}

.portSelect {
    display: flex;
    flex-direction: column;
}

/* phpmailer diagnostic output section */
.diagOutput {
    border: 1px solid black;
    height: 250px;
    margin: 0 auto;
    max-height: 250px;
    overflow-y: auto;
    padding: 8px;
    width: 85%;
}