Change ion-input underline color in Ionic 4 - ionic-framework

Question

How can we change the default underline color of a ion-text in only a single page in Ionic 4?

Answer 1

The underline is actually a part of the ion-item, not the ion-input.
ion-item {
--border-color: var(--ion-color-danger, #f1453d);
}

Answer 2

Ionic 4.x uses CSS Custom Properties for most of the time.
src/app/pages/test/test.page.scss
:host {
ion-item {
--border-color: white; // default underline color
--highlight-color-invalid: red; // invalid underline color
--highlight-color-valid: green; // valid underline color
}
}
If necessary, please check the other custom properties here.

Answer 3

For Ionic V4.X is a little bit diffrent.
You can open specific_page.scss file where you want to change ion-input border when input value is Valid o Invalid
Change the colors of the following class, like this:
:host {
.item-interactive.ion-invalid{
--highlight-background: yellow !important;
}
.item-interactive.ion-valid{
--highlight-background: black !important;
}
}

Answer 4

Try this css
.item-has-focus{
--highlight-background: #e2e2e2;
}

Answer 5

To aggregate in app.scss file
.ios {
.item-has-focus.ion-invalid {
--border-color: var(--ion-color-danger, #f1453d);
}
.ion-valid {
--border-color: var(
--ion-item-border-color,
var(--ion-border-color, var(--ion-color-step-150, rgba(255, 255, 255, 0.8)))
);
}
.custom-item {
--background: transparent;
color: #fff !important;
--background-focused: transparent;
}
}
.md.custom-item {
--background: transparent;
color: #fff !important;
--background-focused: transparent;
--border-color: var(--ion-item-border-color, var(--ion-border-color, var(--ion-color-step-150, rgba(255, 255, 255, 0.8)))
);
}
Or use class to you custom .custom-item.hydrated.ion-touched.ion-dirty.ion-invalid.item-label.item-interactive.item-input.item-has-focus.item.ios.ion-focusable